Paraffin alkylation process



NOV. 26, 1946' R. B. THOMPSON Erm. 2,411,817

n PARAFFIN ALKYLATION PROCESS Filed sept. .'50,l 194:5

'Patented Novias, 194e PARAFFIN ALKYLATION PROCESS Ralph B. Thompson and Joseph A. Chenicek,

Riverside, Ill., assignors to Universal Oil Products Company, Chicago, lll., a corporation of Delaware Application September 30, 1943. Serial No. 504,462

` 10 Claims.y (Cl. Zim-683.4) l 2 This invention relates to the alkylation of isoto the alkylation zone. Therefore, ethyl chloride parailins with oleilns in the presence ofan alulcan be recycled indeiinitelyv in the system with minum chloride catalyst. The invention is more the addition of relatively small amounts of makespeciilcally concerned with certain improvements up hydrogen'chlorlde to compensate for mechaniin the production of valuable hexanes by the al- 5 cal losses, etc. kylation of isobutane with ethylene. In a broad aspect the present invention relates It is known that valuable hexanes'can be proto the use of ethyl chloride as a promoter for duced by the interaction of isobutane with ethaluminum chloride catalysts in the alkylation of ylene. When this alkylation is conducted in the isobutane with ethylene. presence of a suitable catalyst, e. g., aluminum 'In one specific embodiment the present nven-v chloride oran aluminum chloride-hydrocarbon tion comprises alkylatlng isobutane with ethylene complex, 2,3-dimethylbutane is obtained as the in the presence of an aluminum chloride cataprincipal alkylation product. This hydrocarbon lyst and ethyl chloride-as a promoter, separating has veryy valuable antiknock properties and is, ethyl chloride from the reaction products, recovertherefore,` desired for use in aviation gasoline ing alkylation products of desired boiling range, blends or other motor fuels. It is generally deand recycling said Separated ethyl chloride to the slrable'to employ hydrogen chloride as a proalkylation step. moter for the aluminum chloride or aluminum 'I'he term aluminum chloride catalyst as used chloride-hydrocarbon complex catalyst. in this specication and appended claims is in- From a commercial point of view, the isobu` 20 tended to include aluminum chloride vper se, alutane-ethylene alkylation process employing an mlnum chloride supported on various relatively ,J

aluminum chloride catalyst presents a diilicult inert carriers, aluminum chloride composited with problem. Since ethylene is not readily available other. lcatalytic materials such as other metal in pureform. it is necessary to employ ethanehalides, and aluminum chloride-hydrocarbon ethylene fractions as a source of ethylene feed. 25 complexes. The preferred method of utilizing These Cn hydrocarbon fractions as produced in aluminum chloride to catalyze the reaction of isovarious hydrocarbon. conversion processes, e. g. butane with ethylene is in the form of a fluid thermal or catalytic cracking, may contain from aluminum chloride-hydrocarbon complex.'` Variabout to about 70 mol per cent of ethylene. ous complexes may be prepared lby contacting ole- If this mixture is charged directly to the alkyla- 30 ilns, aromatics, naphthenes, parailins, or mixtion zone, a gaseous fraction is separated from the tures thereof with aluminum chloride under suitalkylation products which comprises unconverted able reaction conditions and preferably in the ethane and hydrogen chloride. The separation presence of hydrogen chloride. It will be apparof hydrogen chloride from ethane in order to ent that a wide variety of complex catalysts may permit recycling ofthe catalyst promoter to the be Prepared dependent upon the particular hyalkylation zone is a relatively inconvenient and drocarbons chosen to react with the aluminumy costly procedure. In order. to avoid this diflichloride, the relative amounts of reactants, the culty it has hitherto been customary to provide reaction conditions, etc. In general we prefer an ethylene concentration unit which by means to employ an aluminum chloride-hydrocarbon of aseries of fractionation steps increases the concomplex of the type which is formed inherently centration of ethylene in the ethane-ethylene when isobutane and ethylene are contacted with feed to the order of 85-95 mol per cent thereby aluminum chloride under alkylating conditions. decreasing the quantity of ethane charged to the .The nature of our preferred catalyst will be dealkylation system and minimizing the ethanescribed hereinafter in greater detail.

hydrogen chloride separation problem. 45 For further explanation -oi. the present inven-a We have discovered that under suitable contion reference is now made to the drawing Whereditions substantially all of the hydrogen chloride in Figure vl is a diagrammatic flow chart of the charged to the alkylation system reacts with ethprocess of the present invention and Figure 2` ylene to produce ethyl chloride. The separation illustrates in detail the preferred arrangement `of the latter compound from unconverted ethane of apparatus for conducting the alkylation step is asimple matter, and the ethyl chloride may in the presence ofapreferred'catalyst. be recycled to the alkylation zone thereby replac- Referring to Figure l, zone I represents an ing hydrogen chloride as a promoter. We have allwlation zone of any suitable typeior effecting found that, contrary to expectation, there is no the isobutane-ethylene alkylation in the presence net consumption of the ethyl chloride recycled of an aluminumchloride catalyst.- lIi.' the catalyst comprises granular aluminum chlorideor supported aluminum chloride, reaction zone l will usually consist of a fixed bed oi' the solid catalyst lthrough which the reactants are passed under withdrawn through line 25 and valve 28. By thus recycling ethyl chloride to the alkylation zone I it will only be necessary to add relatively minor amounts of make-up hydrogen chloride through line 6 in order to compensation for mechanical losses, certain ineiliciencies in the separation steps, etc.

As an alternative method of operation all or a yportion of the normal butane-ethyl chloride valve 3. An ethane-ethylene fraction is admitted through line 4 containing valve 5. Hydrogen chloride may be introduced to alkylation zone I through line 6 and valve 1. In the isomerization of normal butane in the presence of AlCla-HCl it is often necessary to discard an ethanehydrogen chloride mixture. In the present invention, however, an ethane-HC1 mixture of this type can readily be supplied through line 6 without the disadvantages previously expected from such a method of operation. 'I'he reaction products are withdrawn from thereaction portion of the system and are introduced through line 8 containing valve 9 to separation zone III which will ordinarily comprise one or more fractionating zones euipped with the conventional condensers, receivers, etc. Unconverted ethane is withdrawn as a gas through line II containing valve I2 and is vented to the atmosphere. In certain cases this discarded ethane fraction may contain relatively minor amounts of hydrogen chloride. Uncoverted isobutane is withdrawn from zone I and recycled through line I3 and valve I4 to line 2 and thence into alkylation zone I. Alkylation products are withdrawn through line I6 containing valve I6 and are subjected to fractionation in zone I1. A lower boiling fraction comprising 2,3-dimethylbutane is recovered through line I8 and valve I9. Higher boiling alkylation products such` as octanes are withdrawn through line containing valve 2|.

As hereinbefore described, we have found that the hydrogenl chloride charged to alkylation zone I is substantially completely converted to ethyl chloride by reaction with a portion of the ethylene feed. vSince ethyl' chloride has a normal boiling point of 12.2C., it may be condensed readily and the unconverted ethane may be vented from the system as a gas. Ethyl chloride forms an azeotrope with .normal butane, however, and in some cases it will be necessary to recover ethyl chloride from the azeotropic mixture in order to recycle the same to the alkylatlon step without the necessity of recycling excessive amounts of normal butane. We have not observed any indications that an azeotrope is formed between isobutane and ethyl chloride. At atmospheric pressure the normal butane-ethyl chloride azeotrope contains approximately 12-13 mol per cent ethyl chloride and has a boiling point almost -identical with. that of pure normal butane.

The normal butane-ethyl chloride azeotrope may be withdrawn from the. separation step through line 22 containing valve 23 and introduced into`a separation zone 24 wherein the ethyl chloride is separated from the normal butane by some suitablemeans other'than by distillation. The separated ethyl chloride is recycled to the alkylation zone through line 21 containing valve 28 and thence through line 6. Normal butane is azeotrope may be recycled directlythrough line 22 and valve 23 to line 6 and thence into alkylation zone I. This operation may be feasible 4when the normal butane content of the butane feed introduced to the system .through line 2 is relatively low, but it will generally be necessary to remove at least a portion of the normal butane from the system by means of separation step 24, or merely by withdrawing a portion of the azeotrope from the system throughline 29 and valve 29.

'.Various methods may be employed in separation step 24 for resolving the normal butaneethyl chloride azeotrope. particularly convenient consists in treating the azeotrope with a selective solvent in which the ethyl chloride is preferentially soluble. In general, polar solvents that are insoluble in butane may be employed in the extraction step. The ethyl chloride may then be recovered from the solvent by distillation. Suitable polar solvents comprise the alcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol, or mixtures thereof. Polyhydroxy alcohols such as ethylene glycol or propylene glycol arealso suitable. Ex-

cellent results are also obtainable using aqueous solutions of the alcohols, particularly ethyl alcohol. ethyl chloride, the azeotrope may be contacted with a dehydrohalogenating catalyst whereby to decompose the ethyl chloride to ethylene and hydrogen chloride. The ethylene -and hydrogen chloride are separated from normal butane and may be recycled directly to the alkylation zone or if desired may be recombined in the presence of a suitable hydrohalogenation catalyst to form ethyl chloride which is then returned to the al lrylation step.

In starting up an alkylation process of the present type two general methods of operation may be employed. Obviously, it is possible to charge ethyl chloride directly to the alkylation zone as a promoter for the aluminum chloride catalyst and when the system contains sufcient ethyl chloride, the addition of make-up hydrogen chloride'may be started. In another method of operation, only hydrogen chloride is charged to the system initially. As the alkylation reaction proceeds the hydrogenv chloride added is almost completely converted to ethyl chloride which is recovered in the manner hereinbefore described and recycled to the alkylation step.

Figure 2 illustrates a preferred arrangement of apparatus for eiecting the alkylation reaction. Zone 35 is a pickup or saturation zone which contains a bulk supply of aluminum chloride usually in the form of granular particles. The isobutane charge is introduced at least in part through line 30 containing valve 3|, pump 32, and line 33 containing valve 34 to the pickup zone 35. This portion of the isobutane charge dissolves aluminum chloride during its passage through zone 35 and the eiiluent stream removed through line 36 and valve 31 is substantially saturated with aluminum chloride. Another portion of the isobutane charge is passed through line 38 and valve 39 and One method which is l As another possible method of separating is commingled with the edluent solution from zone as shown. The mixture is charged to alkylation zone I0. If ldesired all of the isobutane charge may pass through zone 35.

The ethane-ethylene charge is introduced to alkylation-zone 40 through line'43 containing valve M. Hydrogen chloride and recycled ethyl chloride are added through'llnerl containing valve 46. Alkylation zone l0 is a mechanically agitated zone provided with' stirring device. driven by motor 42. During the alkylation reac- .tion in zone 40 the fresh aluminum chloride introduced from pickup zone-35 is converted to a iluid aluminum chloride-hydrocarbon complex.

The eilluent mixture of catalyst andreactionf products is passed through line 4l and valve I8 to settler 49 from which an upper hydrocarbon layer is withdrawn to further separation steps through line containing valve 5I and a lower catalyst ,layer is recycled to the alkylation zone through line 52 containing valve 53. pump 50, and line 55 Acontaining valve 56. .A portion of the used catalyst may be withdrawn from the system through line 51 containing valve 58.

' In the system described in connection with Figure 2 it will be apparent that the aluminum chloride content ofthe aluminum chloride-hydrocarbon complex catalyst in alkylation zone v40 CTI time (defined as volume of catalyst in the reacl tion zone divided by the volume rate per minute of hydrocarbon feed) of 28 minutes was employed at a temperature of F. and a pressure of 250 poundsper square inch gage. The pickup zone was operated at F. and 250 pounds per square inch 888e.

During this operation a yield of `hexanes of 193 weight per centgbased on the ethylene charged may be controlled accurately by the addition of F. to 140"- F., and under suicient pressure to maintain at least' a portion of the reactants in the liquid phase. It is also desirable to maintain an appreciable mol excess of isobutane overeth'- ylene -in the hydrocarbons charged to the alkylation step, e. g.'from-about 4:21 to about 20:1.

The following experimental data are presented in order to demonstrate the nature ofthe present invention. It is -by no means intended, however. to limit the scope of the invention by the details of these examples. All of the experimental data described in these examples were obtained in an apparatus substantially of the type showndn Figure 2 of the drawing. Suitable stabilization equipment was provided for treatment of the hydrocarbon products withdrawn through line 50.

' Example I During a 48 hour period isobutane was alkylatedvwith ethylene in the presence of the aluminum chloride-hydrocarbon complex formed in situ. The charging stockv to the alkylation -zone had the following compositionA on a mol per cent basis:

Per cent Propane; e-.e 1.3 Isobutane '-e 59.5 n-Butane 24.8 Pentanes 0.2 Ethylene 12.1 Hydrogen chloride 2.1

was obtained. The hexane cut had a chlorine content of 0.0002 weight per cent. l

In an attempt to obtain a weight balance on the hydrogen chloride charged to the systeml the ei'iluent gas from the stabilization step was scrubbed with a measured volume of sodium hydroxide and the excess base titrated with lhydrochloric acid. In three such determinations made during the .run the hydrogen chloride in the emuent gas was found to beonly 0.01-0.02 'gram per hour whereas the rate of introduction of hydrogen chloride to the alkylation system was approximately 1.8 grams per hour. From these results it is apparent that most of the hydrogen chloride was converted to organic chlorine containing compounds during the alkylation re action.

Example II In a further attempt to explain the apparent consumption of hydrogen chloride observed in Example I similar alkylation runs were made and the 'distribution of chlorine was. determined in the various products. rThe results of the chlorine determinations are summarized as follows:

Distribution of chlorine in ethylene-isobutane alkylation Period number Cl in stabilizer overhead grams.. 64.92 60.92 60.87 Fl in C. from alkylaie do.... 2. 78 1.48 Cl in total alkyiate .do...` 0.06 0.12

' 'rmalolremvered ..do.... o1 1s 62.52

bil

A volume. ratio 'of catalyst to hydrocarbon in the alkylation zoneof 0.88 was maintained. A space It will be evident that most of the chlorine was found in the lower boiling compounds removed overhead during the stabilization step. By means of a careful low temperature Podbielniak fractionation, the chlorine in the stabilizer overhead was found to be present as ethyl Chloride.

`Further evidence thatethyl chloride is formed during the reaction was obtained in a series of runs in which the amount of hydrogen chloride charged to the process' was varied. As the rate of introduction of hydrogen chloride was increased the yield of alkylate based on the ethylene charged decreased thus indicating substantial reaction of the hydrogen chloride with ethylene. Yields calculated on the basis of ethylene available afterreaction with hydrogen chloride were approximately the theoretical yields.

Example III In order to demonstrate that ethyl chloride can be recycled to the alkylation zone and that it will serve as a promoter for the aluminum chloride-hydrocarbon complex catalyst without net consumption, the following test was made employing substantially the same apparatus andA method of operation as described in connection with ExampleI.

'i' The combined feed charged to the alkylation zone had the following mol per cent composition:

The reaction was carried out at a temperature of 140 F.a pressure of 250 pounds per square inch gage, a space time of 29 minutes, and a catalyst to hydrocarbon volume ratio of about 0.7. The pertinent results over 322 hours of operation are summarized as follows:

ethane feed stock since any ethane present in the feed can be separated from ethyl chloride after alkylation of the ethylene. The recovery of ethyl chloride from its azeotrope with normal butane is a relatively simplematter and can generally be accomplished with no more difculty than the hydrogen chloride-'ethane separation step which was previously considered necessary.

An additional advantage attendant upon the use of ethyl chloride as a promoter for aluminum chloride alkylation catalysts, particularly the aluminum chloride-hydrocarbon complex catalysts, is the low corrosion rate. When hydrogen chloride isemployed as a promoter` there is often Period No.

Length of period v houlS.. 48 48 42 Cumulative time do 93 131 250 322 Yield of alkyiate, weight per cent of C2H4 charged 304 304 1 214 1 228 Volume per cent hexanes in alkylate 73. 6 77. 4 79. 9 80. 4 Chlorine, weight per cent of Ce product 0.0022l 0.0014 0. 00l7 0.0014 Ethyl chloride weight balance:

CzHCl charged.. grams 75,6 64.8 74.8 CrHCl recovered. do.. 75. 2 68. 5 l76. 9

i Yields uncertain because of operating difficulties.

The 304 weight per cent alkylate yields in periods l and 2 is approximately the theoretical yield of 307 weight per cent indicating that all of the ethylene charged was available for alkylation. This is in marked contrast to the results obtained with hydrogen chloride as a promoter in which case a portion of the ethylene reacts with the hydrogen chloride charged and is, therefore, unavailable for alkylation.

The calculation of the ethyl chloride. recovered was based upon the chlorine analysis of the stabilizer overhead assuming total recovery of unreacted hydrocarbons. The ethyl chloride charged to the reaction was calculated from the chlorine analysis of the entering charging stock. Within the experimental error of the operating technique and the analytical methods, the data indicate that there is no appreciable consumption of ethyl chloride during the reaction. The fact that only traces of ethane, if any, are found in the stabilizer overhead leads to the conclusion that consumption of ethyl chloride' by halogen exchange with isobutane does not occur to any great extent. It will be apparent that in continuous operation on a commercial scale ethyl chloride lost by mechanical means, etc. can be replaced by the addition of a small amount of hydrogen chloride to the system.

We have discovered that an ethyl chloride concentration within the range of from about 0.6 mol percent to about 2.5 mol percent of the hydrocarbons charged is required for promoting the alkylation of isobutane with ethylene.

It will be apparent that the process of our invention wherein ethyl chloride is formed in situ by the reaction of hydrogen chloride with ethyla pronounced tendency toward -corrosion of reaction equipment dependent upon temperature of operation and concentration of hydrogen chloride. l

We claim as our invention:

1. An. alkylation process which comprises introducing isobutane and 'an ethane-ethylene fraction to a reaction zone and therein reacting a substantial portion of the ethylene with iso- .'butane in the presence of an aluminum chloride catalyst, supplying tosaid zone an amount of hydrogen chloride not substantially in excess or' that which will react with the remainder of said ethylene and therein reactingsubstantially all ofI the hydrogen chloride with ethylene to form ethyl chloride in the reaction zone, removing the reaction products from said zone and separating ethyl chloride from the hydrocarbon alkylate and the ethane content of saidfraction, and recycling thus separated ethyl chloride to the reaction zone, the amount of ethyl chloride formed in and recycled to said zone being suiclent to promote the isobutane alkylating reaction therein.

2. An alkylation process which comprises introducing isobutane and an ethane-ethylene fraction to a reaction zone and therein reacting a substantial portion of the ethylene with isobutane in the presence of an aluminum chloride catalyst, supplying to said zone an amount of hydrogen chloride not substantially in excess of that which will react with the remainder of said ethylene and therein reacting substantially all of the hydrogen chloride with ethylene vto form ethyl chloride in the reaction zone, removing the ene and is then recycled to the reaction zone reaction products from said zone and separating ethyl chloride from the hydrocarbon alkylate and the ethane content of said fraction, recycling thus separated ethyl chloride to the reaction zone, and regulating the amount of ethyl chloride recycled and the amount of hydrogen f chloride introduced to said zone to maintain the ethyl chloride concentration in the reaction zone within the range of from about 0.6 to about 2.5 mol percent of the hydrocarbon reactants charged to said zone.

3. An alkylation process which comprises introducing an ethane-ethylene fraction and a heavier fraction containing iso and normal butanes to a reaction zone and therein reacting a substantial portion of the ethylene with isobutane in the presence of .an aluminum chloride catalyst, supplying to said zone an amount of hydrogen chloride not substantially in excess of that which will react with the remainder of said ethylene and therein reacting substantially all of the hydrogenI chloride with ethylene to form ethyl chloride in the reaction zone, removing the reaction products from said zone and separating ethyl chloride therefrom in the form of an azeotrope with normal butane, and recycling at least a portion of the ethyl chloride content of said azeotrope to the reaction zone. the amount of ethyl chloride formed in and recycled to said zone being sulcient to promote the isobutane alkylating reaction therein.

4. The process as deined in claim 3 further -characterized in that said portion of the ethyl 8. 'I'he process oi claim 1 wherein said. catalyst consists essentially of an aluminum chloridehydrocarbon complex formed by contacting isobutane and ethylene with aluminum chloride under alkylating conditions.

9. The process of claim 3 wherein said normal butane-ethyl chloride azeotrope is extracted with a solvent in which ethyl chloride is preferentially soluble and ethyl chloride is subsequently separated from the extract and recycled to the reaction zone.

l0. The process of claim 3 wherein said normal butane-ethy1 chloride azeotrope is eirtracted with an alcohol in which the ethyl chloride is preferentially soluble and ethyl chloride is subsequently separated from the alcoholic extract by distillation and recycled to the reaction zone.

RALPH B. THOMPSON.

JOSEPH A. CHENICEK. 

